gms | German Medical Science

Objectives: The pathogenetic link between osteoarthritis (OA) and diabetis mellitus type II (T2DM) remains still unknown. Complement dysregulation is involved in the pathogenesis of OA and might also play a role in T2DM. The anaphylatoxin C5a is released in response to complement activation and could exert inflammatory cell responses. However, the effect of T2DM on complement regulation remains unclear.

The aim of this study was to understand the specific responses of chondrocytes isolated from non diabetic and diabetic rats exposed to the proinflammatory cytokine TNF-α and C5a in vitro dependent on the glucose supply.

Methods: Articular chondrocytes were either isolated from the knee joints of adult non diabetic Zucker Diabetic Fatty (ZDF) rats (fa/+) or those rats (fa/fa) showing the crucial symptoms of T2DM. Cultured chondrocytes were exposed to 10 ng/mL TNF-αand 25 ng/mL C5a alone or in combination, both, under normo- (NG) and hyperglycemic (HG) conditions (1 g/L versus 4.5 g/L glucose, 4 or 24 h stimulation). Chondrocyte survival and metabolic activity were determined. Gene expression of collagen type II, suppressors of cytokine signaling (SOCS)1, -3 and hemoxygenase-1 (HMOX1) was assessed by real time PCR after 4 or 24 h. The complement regulatory protein CD46 was detected by immunolabeling (24 h) and the volumes of cell nuclei were calculated based on 4,6-Diamidin-2-phenylindol (DAPI) stain (24 h).

Results and conclusion: Chondrocyte vitality was not affected by the treatment regime but the metabolic activity was generally impaired in chondrocytes derived from diabetic rats under NG and HG conditions. Collagen type II gene expression was suppressed by TNF-α under HG condition in unstimulated chondrocytes and under both regimes in T2DM chondrocytes after 24 h.

Except for cultivation of T2DM chondrocytes under HG for 4 h, the antioxidant defense enzyme HMOX1 was generally induced in chondrocytes treated with TNF-α alone or in combination with C5a in T2DM and non diabetic animals under both conditions. C5a induced HMOX1 only in non diabetic chondrocytes. The SOCS1 and SOCS3 genes regulating negative feed-back loops of cytokine signaling were generally induced by TNF-α under NG condition irrespectively whether chondrocytes derived from non diabetic or T2DM animals at both time points and after 24 h exposition to HG in diabetic, but not in non diabetic chondrocytes. At 4 h C5a induced SOCS1 only in non diabetic chondrocytes but under both glucose levels. CD46 protein synthesis was generally suppressed by TNF-α under NG condition. Nuclear volumes of chondrocyte were generally lower in chondrocytes from T2DM rats compared to those from non diabetic animals suggesting differential effects of the glucose levels on chondrocyte cell cycle.

The response of chondrocytes to TNF-α and the anaphylatoxin C5a differs dependent on the glucose supply and their origin from non diabetic and diabetic donors in regard to regulation of cytokine signaling.